Large diameter pipe causes the air to slow down. Velocity suffers and when it slows, you know 14.7 is heading back in.
We have a war going on with 14.7psi. What is the pressure in the exhaust pipe when the engine is dead? 14.7psi. What happens when we push a low pressure out is say half the air is 8lbs? Say, 7 plus 7 is 14. Say, 8lbs.; give or take is half of 14.7? Do we see our war game on the valve close and open?
How much back pressure will 14.7 take in time and in more or less, the larger the pipe, the slower the one air goes, the faster the other takes is that sound wave. Each cylinder is a snowflake of a pressure wave. Say, a compression reading on one cylinder is 187psi, and the cylinder next to it pushes the compression needle to 178.
No matter the argument, I cannot smooth the walls any less porous for the rings, the gap is the same; the cc chamber is the same; we compile all that even up on each cylinder and each compression is not the same. Would I now equal length the same length for 2 different compressions? Would they not burn or move the air speed differently where equal length is out the window is not equal compression?
On the critical air speed, what I've read that makes sense is that you want no more than a 9° bend out of the header from exhaust valve. You want the straightest direction possible for as long as possible, or a bend will slow down the flow. Imagine the short curve out of the pipe we are looking at. The radiator will not let that bend move out farther in a straight line.
Smarty pants also receives no credit for the PAIR system along with his 4-in-1. Smokey knew about fresh air entering the exhaust pipe, so he drilled tiny holes under the exhaust so no one would see the theory that if you let fresh air back in, you reburn the unspent, keep 14.7 from reentering too fast is push more heat flow = Keep the spent moving.
Pipe Tie-in on Phil's post, I have to disagree with what I have read, is that if you tie-in both sides, you have a better short track exhaust. If you have them duals/separate and open, they are more for Daytona or Taladega.
When I changed from a 4-in-1, I could feel the duals were a much smoother in combination. The difference is slight, mind you, so it is more what that balance the tie-in represents; is a better air blend. What I found out between the two combo'z; are that the single pipe pops less. That guess would be the unspents are combined in a short area, where as, the dual separates into a larger area of mass. So, rich is 4-in-1. Lean are duals? One test ride does not qualify my theory. But to change very few things as one muffler is little to nil and note the change in popping. You have received the raw data. You can come to your own conclusion. I am 'butt' the messenger.
http://www.youtube.com/watch?v=mhpjw6iqFaA&feature=fvw We are down to trick looks. Cool sounds? Give me a fender washer and a wheel bearing... I got year muffler, fell ear.
Tormenting the motorcycling community one post at a time